Staten Island is so large you could run a marathon on the levee circling its vast cornfields. And yet, by car, there is only one way in and one way out.

Abundant food, plenty of privacy - all the better for the sandhill crane.

"They're not disturbed much here, and that's partly why they like it," land manager Dawit Zeleke said at sunset earlier this week as his car slowed to a stop adjacent to a flooded field. Even his quiet Prius was enough to startle some of the cranes into taking flight.

Gov. Jerry Brown's proposed water diversion tunnels would pass perhaps 150 feet beneath this very spot, raising questions among crane admirers how this majestic and ancient species - whose numbers have declined over the decades - could coexist with a multiyear industrial project of that magnitude.

State officials have assembled a team of crane experts as consultants. They say the disruption will not be as significant as birders might expect. The 9,100-acre island north of Highway 12 is so large that the cranes wintering there should still have room enough to forage and roost, even as the work commences.

It is difficult to know how any species might react to new disturbances, said Mike Bradbury, an avian ecologist and program manager for the state Department of Water Resources.

"But I think that by the time we get done with the final designs and construction plan for Staten Island, we're going to have a plan where the cranes do very well out there," Bradbury said.

Mike Eaton, a crane advocate who worked for The Nature Conservancy when that environmental group purchased Staten Island in 2001, is skeptical. Cranes have already seen much of their territory swallowed up by sprawling cities, and many farms are converting from row crops to more lucrative vineyards and orchards, which do not provide the habitat cranes need.

Eaton said he thinks it's "theoretically possible" to protect cranes from the impacts of building the tunnels but says details about how this would be accomplished are missing.

"Yes, they have goals, ... but there is no content at all in terms of how you get from A to B," Eaton said. "It's like the publicists are writing the plan and the scientists are lagging."

One of San Joaquin County's largest tracts of farmland, Staten Island was once owned by a real estate company based in Portland, Ore. It was farmed by Jim and Sally Shanks, whose wildlife-friendly practices gave safe harbor to an estimated 20 percent of the cranes that visit the Central Valley each winter.

When the Shanks retired, The Nature Conservancy bought the island using about $30 million in public grants awarded by the state, which also obtained an easement requiring wildlife-friendly farming to continue there.

"We thought we were saving it for the cranes," Sally Shanks said in a phone interview this week. "We thought it would be their last bastion. Now look what's happening. It's very disappointing."

The $14.5 billion tunnels would divert some Sacramento River water underneath the Delta rather than allow it to flow through the estuary. The idea is to establish a more reliable water supply for much of the state. Billions more would be spent on efforts to improve the Delta's ecosystem by restoring habitat for wildlife, including cranes.

The tunnels were originally slated to cross the Delta farther west. In August the state announced a change in the alignment, reducing harm to communities along the Sacramento River but also moving the project closer to the cranes.

With the guidance of crane experts, however, even more changes have been made since the new alignment was announced, the state says.

Muck unearthed by giant tunnel boring machines is no longer expected to be piled across 1,274 acres on the southeast corner of the island.

Much of the construction activity will be shifted to the north end of the island, an area less likely to be used by cranes. And as much of that work as possible will take place during the spring and summer when the cranes are absent.

Harvested cornfields will be strategically flooded to help returning cranes find a new place to roost, should their favorite fields from past winters no longer be available.

And some fields might not be harvested at all, increasing the amount of food and allowing more foraging in a smaller area.

For the long term, the tunnel plan calls for 48,000 acres of farmland throughout the Delta to be preserved through conservation easements, with 7,000 acres of that land designed to help cranes.

As for the tunnel machines themselves, the deep drilling seems unlikely to bother the birds, Bradbury said. Cranes in the Delta are used to the slow, constant noises often associated with agriculture - it's more the sudden, unexpected noises that might frighten them, he said.

"The one thing that I think needs to be addressed is this idea that the construction would result in this catastrophic loss of use of Staten Island," Bradbury said. "I think that kind of thinking comes from people that don't understand the biology of the bird very well. The experts we work with, nobody thinks that's going to happen."

Still, sandhill cranes have not been exposed to a construction project of this scope in the past, said Sacramento biologist Paul Tebbel, who worked with cranes for more than a decade at a refuge on the Platte River in Nebraska.

If the cranes are unhappy with the fields that are available, they will find someplace else that might not be as safe from people or predators.

And satisfying cranes is not always easy. For example, they demand flooded fields in which to roost, but the water should be only about 4 inches to 6 inches deep.

"They don't like to get their skirts wet," Tebbel said.

Experts at the Nebraska refuge did the best they could to create high-quality habitat for cranes. "But when we screwed up ... we immediately saw the cranes react and move to other locations," Tebbel said.

So when it comes to Staten Island and the tunnels, he said, "Everybody's speculating. We don't actually know what's going to happen."